Method and valve apparatus for controlling a reciprocatable fluid actuated power machine

ABSTRACT

A method and an apparatus for controlling the function of all kinds of reciprocable power machines which are actuated by pneumatic, hydraulic of any other pressure fluid, irrespective if the machines are of rotary or axially operating type, in which the active power stroke is accomplished using full power of pressure fluid against a reciprocatable piston (2) in the active air pressure chamber (10, 12), and in which the reversing of the direction of operation is made by alternatingly supplying pressure fluid to the opposite air pressure chamber (12, 10) of the machine. A valve poppet (6) having several channels alternately places one of the pressure chambers (10, 12) of the reciprocatable fluid actuated machine (1, 2) under full pressure, builds up a certain counter pressure in a pressure chamber which is, at the actual moment, inactive, and evacuates the pressure from an inactive pressure chamber of the fluid actuated machine.

The present invention relates to a method and an apparatus forcontrolling the function of a reciprocatable fluid actuated powermachine. By fluid actuated power machine is meant, in this connection,all kinds of reciprocatable machines which are actuated by means ofcompressed air, hydraulic oil or any other fluid, irrespective if saidmachines are of rotatably or axially operating type, and which canexecute its power in two opposite directions, or the machine executesits power in one direction only followed by a return movement withoutpower execution, and whereby the reversing of direction is made byreversing the direction of the compressed air or the hydraulic fluid inthe active part of the machine. So, the invention is useful both forsingle acting and double acting reciprocatable fluid actuated powermachines.

In the following the invention will mainly be discussed in connection topneumatically operated cylinder-piston units. It is, however, to beunderstood that this is only illustrative examples which do not restrictthe invention. Be it known that the invention is as well useful both forlinearly operated machines as for rotating machines and for machinesoperated by compressed air, hydraulic oil or any other fluid.

There are three basic problems of known reciprocatable pneumatic andhydraulic machines both of the single acting and of the double actingtype, which problems form basis of the present invention. Said problemsappear to the same extent both in rotary operating machines as inaxially operating, reciprocatable machines, generally referred to as"compressed air cylinders" or "hydraulic cylinders", but for the sake ofsimplicity, as mentioned above, the invention will be described in thefollowing only with reference to a pneumatic piston/cylinder unit ofreciprocatable type.

All three different main problems, which appear in reciprocatable,pneumatic power machines, are related to the reversing phase, duringwhich phase the active part of the machine, in the described case thecompressed air piston, is to reverse its direction of operation. This ismade in that the compressed air is switched from having acted on oneside of the piston to acting against the opposite side of the piston.

When reversing the direction of function in previously known apparatusthe compressed air is evacuated from the side of the piston which is theactive side until the moment of reversal in that the pressurised workingchamber is evacuated at the same time as compressed air is supplied tothe opposite side of the piston:

1) firstly, this makes the often very strongly compressed air pressureat the unloading phase create an air blow which is received as anoftenly very high sound or bang, which can be very disturbing;

2) secondly, depending on the momentary draining of the pressure in theair chamber which has so far been pressurised, some amount of compressedair gets lost; such loss of compressed air means an economical loss ofvalue considering the costs and the work for producing said compressedair;

3) thirdly, at the same time as one of the compressed air chambers isbeing evacuated and the opposite compressed air chamber is pressurisedby means of the oftenly high air pressure, the piston is immediately ormomentarily stopped and momentarily thereafter starts moving in theopposite direction with high speed and high power. This may in somecases cause problems. Said problem also appears in hydraulicallyoperated machines.

Still another problem in pneumatic power machines is to have the activepart thereof, generally the piston, stop in a predetermined position. Amain reason for this problem is the compressibility of the air.

In single acting reciprocatable cylinders the power stroke is made bymeans of compressed air, whereas the return movement is generallyaccomplished by means of return spring. In order to overbridge the powerof the return spring it is necessary to make use of a substantiallystronger power of the compressed air or the hydraulic fluid than wouldhave been needed if the cylinder had no return spring.

The object of the invention therefore is to eliminate all of the abovementioned problems and disadvantages by suggesting a simple method and asimple type of valve arrangement, and thereby to suggest a method and anapparatus in a reciprocatable, single or double acting fluid actuatedpower machine:

a) which to a high extent reduces the noise which is created at theevacuation of the air pressure when the active part of the power machinereverses its operation direction;

b) which makes it possible to save at least 30-50% of compressed air ofthe previously needed amount of fluid;

c) which makes the active part of the pneumatic or hydraulic powermachine both stop and start relatively softly during the reversingphase;

d) and which makes it possible to stop the piston movement ratherexactly at any point of the piston/cylinder unit.

According to the invention this is generally accomplished in that thepiston of the fluid actuated machine meets a counter pressure both atthe end of an active power stroke and at starting of a power stroke inthe opposite direction. The soft braking preferably is made in that thetwo sides of the fluid actuated machine are interconnected over a shuntshortly before the active part of the machine (the piston) reaches theend of its active stroke whereby the piston softly becomes braked. Theshunting, or the equalization of the compressed air can be made inseveral successively increased stages, using mechanical or other typesof pressure restricting valves to complete equalization of power at bothsides of the piston.

In a double acting cylinder the function of the piston, during thereversing of the working direction is split into eight different phases,namely, starting from a full speed working phase in one direction:

A. a full speed working phase in a first direction (→), during which thepiston is moved in a predetermined direction (e.g. as shown in FIG. 1);

B. a soft stopping phase (FIG. 2) during which the piston movement issoftly braked to stop;

C. an equalizing and reversing phase (FIG. 3), during which the twopressure chambers are subjected to the same pressures;

D. a soft starting phase (FIG. 4) during which the piston starts movingin the opposite direction (←) against a slight counter pressure which issuccessively reduced to atmospheric pressure;

E. a full speed working phase (FIG. 5) at full pressure in said oppositedirection (←);

F. a soft stopping phase (FIG. 6) during which the piston movement issoftly braked to stop;

G. an equalizing and reversing phase (FIG. 7), during which the twopressure chambers are subjected to the same pressures;

H. a soft starting phase (FIG. 8) in a reversed direction during whichthe piston starts moving in said first direction (→) against a slightcounter pressure which is successively reduced to atmospheric pressure.

The function is illustrated in the following table 1:

                  TABLE 1                                                         ______________________________________                                        (reversible power type)                                                             shown    left     right  actual                                               in       chamber  chamber                                                                              function                                             FIG.     pressure pressure                                                                             of the                                         phase nr       (P)      (P)    phase   next phase                             ______________________________________                                        A     1        full P   0      full    soft                                                                  speed →                                                                        stopping →                      B     2        full P   choking ↓                                                                     soft    stop/                                                                 stopping →                                                                     reverse                                C     3        0        0      stop/   soft                                                                  reverse .OR left.                                                                     starting ←                        D     4        choking ↑                                                                        full P soft    full                                                                  starting ←                                                                       speed ←                           E     5        0        full P full    soft                                                                  speed ←                                                                          stopping ←                        F     6        choking ↓                                                                       full P soft    stop/                                                                 stopping ←                                                                       reverse .OR right.                     G     7        0        0      stop/   soft                                                                  reverse .OR right.                                                                    starting ←                        H     8        full P   choking ↑                                                                      soft    full                                                                  starting →                                                                     speed →                         ______________________________________                                    

In a single acting pneumatic cylinder the above mentioned shunt powercan, according to the invention, be used as a return power for thepiston by draining the power of the former pressure side. To this endthere is used a four-stage valve means having four positions providingfive functional phases. The function thereof is illustrated in thefollowing table 2:

                  TABLE 2                                                         ______________________________________                                        (single acting power type)                                                         shown   left     right  actual                                                in      chamber  chamber                                                                              function                                              FIG.    pressure pressure                                                                             of the                                           phase                                                                              nr      (P)      (P)    phase    next phase                              ______________________________________                                        A    12      full P   0      full speed →                                                                    soft                                                                          stopping →                       B    13      0        0      no power equalization                                                         supply                                           C    14      P/2      P/2    stop/reverse .OR left.                                                                 return                                                                        starting ←                         D    15      0        P/2    return mov. ←                                                                     soft starting →                  E    12      full P   P/2    soft starting →                                                                 full speed →                     ______________________________________                                    

Now the invention is to be described in detail with reference to theaccompanying drawings, in which FIGS. 1-8 show a sequence of the abovementioned eight functional phases for a double acting, reciprocatablepneumatic machine, in which FIG. 9 diagrammatically illustrates arotatable valve for performing the soft stopping and soft startingfunction of the pneumatic or hydraulic power machine, and in which FIG.10 illustrates pictures used for marking of the three pressures in FIGS.1-8. FIG. 11 is a diagrammatical view of a 4-stage valve for performingthe operation of a single power operation pneumatic machine, and FIGS.12-15 diagrammatically illustrates the function thereof. FIGS. 16-18illustrate an example of a pneumatic piston-cylinder unit for executingthe method illustrated in FIGS. 12, 14 and 15, respectively.

The operation method of a reversible type power pneumatic or hydraulicpiston-cylinder of the invention is explained in connection to the FIGS.1-9 of the accompanying drawings, which diagrammatically show apiston/cylinder unit comprising a cylinder part 1 and a piston part 2having a piston rod 3, connections 4 and 5 for a pneumatic or hydraulicpressure fluid at each end of the cylinder 1, and a valve 6 for creatingthe various functional phases of the apparatus.

The valve 6, which in the illustrated case is of rotatable type, butwhich may as well be of axially reciprocatable type, is formed with apressure distributing means 7, a means 8 for providing a choking or ashunting of the pressure chambers of the power machine, for instance thepiston-cylinder unit, valve, and a means 9 for evacuating the pressurechambers of the cylinder 1, 2. The valve is illustrated only withrespect to the function thereof in FIGS. 1-9, be it obvious to theexpert how to design the valve in order to obtain such functions.

During its operation the valve of FIGS. 1-9, in the illustrated case cantake eight different active positions marked with letters A-H in FIGS.1-8 respectively.

A. Working phase (direction ), shown in FIG. 1:

We have chosen to start the description of the function in a valveposition (FIG. 1) in which the piston chamber 10 at the stationarymounted side 11 of the cylinder 1 is under full working pressure. Thepressure fluid connection 4 at said stationary end of the cylinder, isconnected the pressure distribution means 7 of the valve 6 placing theouter piston chamber 10 is under full pressure. The piston (rod) chamber12, which is now inactive, is drained in that the pressure fluidconnection 5 at said side of the cylinder is open to the ambient via theevacuation means 9. The piston 2 is thereby forced with full power tothe right as shown in FIG. 1.

B. Soft stopping (equalization, direction ) phase, FIG. 2:

After the valve 6 has been rotated a certain step (45° as illustrated inthe drawings) in the clockwise direction, as shown in FIG. 2, thepressure fluid connection 4 is still under full pressure from thepressure distributing means 7. When the piston 2 approaches the pistonrod end of the cylinder a counter force is applied to the piston rodchamber 12. There are basically two methods of providing such counterforce:

a) to create a slight air or hydraulic pressure in the piston rodchamber 12 from the final movements of the piston 2 the choking means 8is sufficiently (such as 100%) choked, which pressure is then stepwiseor successively decreased, and concurrently therewith stepwise orsuccessively decreasing the pressure in the outer piston chamber 10 sothat the piston 2 is softly brought to stop;

b) for use in pneumatic machines, to break the air pressure to the outerpiston chamber 10 and immediately thereupon to open a bypass or shunt 13(marked with dotted lines in FIG. 2) between the outer piston chamber 10and the piston rod chamber 12, whereby the pressure from the outerpiston chamber 10 is distributed with equal force also to the piston rodchamber 12, whereby there is an equalization of pressure in said twochambers 10 and 12 and the piston 2 is softly brought to stop during theequalization.

C. Inverting phase (direction .OR left.), FIG. 3:

In this third phase the valve 6 has rotated (45°), whereby both theouter cylinder chamber 10 and the piston rod chamber 12 are beingblocked or are opened to the ambient over the evacuation means 9. Nowthe piston 2 is balanced from both sides and is ready to start moving inthe opposite direction.

D. Soft starting phase (direction ), FIG. 4:

The outer piston chamber 10; a) is connected to the choking means 8,whereby said chamber is closed and is thereupon stepwise or successivelyopened to the ambient, whereas the piston rod chamber 12 is subjected tofull pressure, and this makes the piston start moving with a softlyaccelerated piston movement; or alternatively b) the piston chamber canbe put under a slight, stepwise or successively decreased counterpressure over the choking means 8. In both cases the piston rod chamber12 is connected to the pressure distributing means 7 supplying fullpressure to the piston rod chamber 12. The pressure of the piston rodchamber 12 is higher than the pressure of the outer piston chamber 10,and the piston softly starts moving to the left, as shown in FIG. 4. Thepressure gradient is stepwise or successively increasing to maximumpressure following the decrease of the choking pressure in the outerpressure chamber 10.

E. Working phase (direction ), FIG. 5:

In this fifth phase the valve poppet 6 has rotated so that the cylinderchamber 12 is put under full pressure over the pressure means 7, and theouter piston chamber 10 is drained to the ambient, whereby the pistonmoves at full pressure and full speed to the left.

F. Soft stopping phase (direction ), FIG. 6:

In this phase the same process as that of point B above is repeated, butwith the piston moving in the opposite direction. The outer pistonchamber 10 is connected to the choking means 8, or the pressure of thepiston rod chamber 12 is distributed to the outer piston chamber 10.Thereby the piston 2 is softly brought to stop.

G. inverting phase (direction .OR right.), FIG. 7

In this phase the same process is repeated as that of step C above butwith the piston being prepared for moving from left to right (.ORright.).

H. Soft staring phase (direction .OR right.), FIG. 8:

In this phase the same process is repeated as that of step D above butwith the piston softly staring to move to the right as shown in FIG. 8.Thereby a complete operation cycle is ended and the cycle is repeatedfrom point A above.

In FIG. 9 it is indicated that the valve 6 can be connected to a motor(depicted in phantom), which can be an electrical or pneumatical motor,for instance a stepping motor and which can operate the cylinder-pistonunit successively until the operation is to cease. The stepping motorcan be arranged to provide any desired number of small steps, e.g. from10-200 steps per 360° rotation. The valve can be rotated stepwise orcontinuously and by different speeds depending on what function isdesired from the cylinder-piston unit.

By choking or breaking the pressure supply to the piston chambers 10, 12it is also possible to make the piston 2 stop and remain still standingin any position in the cylinder 1 between the end positions, therebyavoiding such "creeping" which can generally not be avoided in pneumaticmachines of conventional type.

In pneumatical power machines it is often difficult to stop the workingmovement in a predetermined position for the piston, among other thingsdepending on the compressibility of the air. According to the inventionthis problem is solved in a pneumatic or hydraulic apparatus or theabove described type in that the deceleration and the stopping of thepiston movement is made in several successive steps with successively orstepwise reduced pressure differences between the working side of thepiston and the evacuated side of the piston. This can simply be made byforming the valve means so as to successively or stepwise choke theevacuation of the evacuated side of the piston, for instance by achoking in four or more steps, like from 100% to 50% to 25% to 0%pressure choking. Said choking can be accomplished in various ways, asobvious to the expert, for instance in that evacuation bores or pressurerestriction valves can be provided in the valve poppet in such positionsand are formed such as to successive or stepwise choking of the piston,starting when the piston has reached a certain position in the cylinder.

Thus, a first choking can be provided to 50% pressure difference betweenthe two piston chambers 10, 12 when there is only about 50 mm left ofthe piston race, a second choking to 25% pressure difference when thereis 10 mm left of the piston race, and a choking to 0% pressuredifference when there is only one or two mm left of the piston race. Thesaid last mentioned "choking step" follows as an addition step after theworking phases according to FIGS. 2 and 6.

In FIG. 11 there is diagrammatically shown a 4-stage valve 15 which ismainly useful for controlling the operation of single power operatedpneumatic machines, like cylinder-piston units. The 4-stage function ofan equivalent sliding value 36, including the air return movement isshown in FIGS. 12-15.

Conventional pneumatical cylinders of this type generally are formedwith a return spring means, at the piston rod chamber side, which makesthe piston return to the stationary side of the cylinder after havingperformed a working phase.

The present valve, which can be mounted at the end of the cylinder, orelsewhere, provides a function eliminating the need of a return springas used in conventional one power stroke pneumatic cylinders. The valveis formed with two discs, a bottom disc 16 and a top disc 17. The bottomdisc 16 is stationary and the top disc 17 is rotatable around a pin 18in relation to the bottom disc. The bottom disc is formed with fourconnections, an air pressure power supply connection 19, a drainingsupply connection 20, a connection 21 to the outer piston chamber and aconnection 22 to the piston rod chamber. The top disc 17 is likewiseformed with four connections 23, 24, 25 and 26 provided similarly to thebottom disc connections. Between the connections 23 and 24 there is abypass 27, and between the connections 25, 26 there is a bypass 28. Thesupply connection 19 is formed with a one-way valve 29 allowing flow offluid only into said connection. In the bypass 27 there is a one-wayvalve 30 allowing flow of fluid only in the direction 23 to 24, and inthe bypass 28 there is a one-way valve 31 allowing flow of fluid only inthe direction 25 to 26. Further there is a first bypass 32 between theouter piston chamber connection 21 in the bottom disc 16 and theconnection 23 of the top disc 17 and a second bypass 33 between theconnections 20 and 24.

The valve 15 makes is possible to make use of an equalization pressureas piston return power. Also in this embodiment there is a soft stoppingfunction and a soft starting function. The function is the following:

Complete stop, FIG. 11

With the valve discs 16, 17, as shown in FIG. 11 there is no supply ofpower from the connection 19; the piston rod connection 5 is closed, andthe outer piston chamber connection 4 is drained.

Power stroke, FIG. 12

After rotating the top disc 17 (in this case 45°) the top connection 25is in line with the power supply 19, and the top connection 26 is inline with bottom disc connection 21. Thereby compressed air is--by asuccessively or stepwise increased pressure gradient--supplied to theouter piston chamber connection 4 via the bypass 28. The piston rodchamber connection 5 is open to the ambient over the connections 22, 23,24 and 20 via the bypass 27.

Intermediate stop position, FIG. 13

At the end of the power stroke the top valve disc 17 is momentarilyrotated to the position shown in FIG. 13, whereby the all bottomconnections and top connections are separated from each other. Thepiston movement is thereby slightly dampened depending on thecompressibility of the air in the cylinder chambers connections 4 and 5.The said intermediate stop position follows during a very short periodof time, for instance only a few parts of a second.

Equalization position, FIG. 14

After a very short while the top disc 17 is rotated to the positionshown in FIG. 14, in which position the power supply 29 is blocked bythe one-way valve 30 in the bypass 27; the drain connection 20 is opento the ambient; the outer cylinder chamber connection 4 is directlyconnected to the piston rod chamber 5 over the connections 21, 25, thebypass 28 and the connections 26, 22. Thereby the pressure from theouter piston chamber connection 4 is distributed also to the piston rodchamber 5, and the piston movement is thereby softly brought to stop. Apressure equalization is obtained between the two piston chambers 4 and5.

Return stroke, FIG. 15

After rotating the top disc 17 another step (45°) the situation appearswhich is shown in FIG. 15, and in which the outer piston chamberconnection 4 is opened to the ambient over the bottom disc connection21, the bypass 32, the top disc connection 25, the bypass 28, the topdisc connection 26 the bypass 33 and the drain connection 20. The pistonrod chamber 5, which is blocked by the top disc connection 22, is stillunder the part pressure obtained during the equalization step. Saidpressure is sufficient for returning the piston to its original positionadjacent the stationary end of the cylinder. Therefore the piston softlystarts moving to the right, as shown in FIG. 15. The pressuresuccessively decreases in the piston rod chamber connection 5 followingthe advancement of the piston, and as a consequence the return speed ofthe piston successively decreases thereby providing a soft stopping ofthe piston adjacent the stationary end of the cylinder. Thereby acomplete operation cycle has come to an end.

FIGS. 16-18 are fragmentary cross section views in the axial directionof one end of a piston-cylinder unit for executing the single powerstroke as illustrated in FIGS. 12, 14 and 15, respectively. In theillustrated piston-cylinder unit both connections 4 and 5 for the inletand outlet of air are arranged at the same end of the piston. The flowof air from the piston rod chamber 12 goes through channels 34 at theperiphery of the cylinder 1. The end head 35 of the cylinder is formedwith a valve poppet 36 and with a passageway system 37, 38 allowing bothinlet of pressurised air, at inlet 4, into the piston chamber 10 andoutlet of air from the piston rod chamber 12, through outlet 5.

The end head 34 is formed with a first passageway 37 communicating theair inlet 4 with the piston chamber 10 and a second passageway 38communicating the piston rod chamber 12 with the outlet 5 over theperipheral channel 34. The valve poppet 36 is slidable in a cylinderchamber 39 in the head 35 and can take two different main positions, apressure position shown in FIG. 16, which corresponds to the valveposition of FIG. 12, and a non-pressure position which is shown in FIG.18, and which corresponds to the valve position of FIG. 15. The valvepoppet 36 is biassed by a spring 40 towards its non-pressurisedposition. The valve poppet is also formed with a cross channel 41 whichin an intermediate position of the valve poppet 36 communicates the mainpiston chamber 10 with the piston rod chamber 12 thereby balancing theair pressure between said two chambers 10 and 12. In said intermediateposition the valve poppet 36 blocks the pressure channel 37 and thedrain channel 38. This intermediate position, which is taken during avery short moment of the return stroke of the valve poppet 36 is shownin FIG. 17. This situation corresponds to the valve setting shown inFIG. 14. The valve poppet 36 also is formed with a bypass channel 42allowing a draining of the piston rod chamber 12 in the pressureposition of the valve poppet 36.

In FIG. 16 is shown that the inlet 4 is pressurised. The air pressureforces the valve poppet 36 to the right, whereby compressed air issupplied to the main piston chamber 10; at the same time the returnchannel 34 from the piston rod chamber 12 is communicated with thebypass channel 42, and the piston 2 is freely moved to the rightcorresponding to the valve setting shown in FIG. 12.

After the piston 2 has been stopped softly at the end of its stroke andthere is no pressure in the inlet 4 or the outlet 5 the spring 40 forcesthe valve poppet 36 back towards its base position. While moving to theleft the cross channel 41 connects the air passageways between the twochambers 10 and 12 to each other for a short moment, as shown in FIG.17. The former air pressure in the main chamber 10 is therebytransmitted to the piston rod chamber 12 over the cross channel 41, partof the end head passageway 38 and the "return" channel 34. In thisposition both the inlet 4 and the outlet 5 are blocked by the valvepoppet.

When the valve poppet 26 has been returned to its initial position, asshown in FIG. 18 the air pressure in the main chamber 10 is drained overthe passageway 37, the cross channel 41 and the outlet 5. The "balanced"pressure still existing in the piston rod chamber 12 is sufficient forsoftly forcing the piston 2 back to its starting position adjacent theend head 35.

Thereby a complete operation cycle is ended. Like in FIGS. 11-15 thereis no need for a return spring or any other means for returning thespring in the illustrated one-way power pneumatic cylinder-piston unit.

What is claimed is:
 1. A method of controlling the function of areciprocatable power machine having a reciprocatable piston locatedbetween first and second pressure chambers, said method comprising thesteps of:moving the piston in an active power stroke from an end of athen active first pressure chamber to an end of a then inactive secondpressure chamber by supplying a pressure fluid at a full power pressureto the then active first pressure chamber; building up a stoppingcounter pressure in the then inactive second pressure chamber as thepiston approaches the end of the then inactive second pressure chamberto counter-act the full power pressure of the pressure fluid in the thenactive first pressure chamber; decreasing of the stopping counterpressure in the then inactive second pressure chamber to a positivefinal stopping counter pressure as the piston reaches the end of thethen inactive second pressure chamber so that the piston is softlystopped at the end of the then inactive second pressure chamber againstthe final stopping counter pressure; utilizing the final stoppingcounter pressure to start an active return power stroke of the pistonfrom the end of a then active second pressure chamber; supplying thepressure fluid at a full power pressure to the then active secondpressure chamber after said utilizing step to move the piston in saidactive return power stroke from an end of the then active secondpressure chamber to an end of a then inactive first pressure chamber;providing a starting counter pressure in the then inactive firstpressure chamber as the piston starts to move from the end of the thenactive second pressure chamber to counter-act the full power pressure ofthe pressure fluid in the then active second pressure chamber, saidproviding a starting counter pressure step including the steps ofthecontrolled opening of the then active first pressure chamber to ambientto fully vent the full power pressure of the pressure fluid as thepiston approaches the end of the then inactive second pressure chamber,and the closing of the then inactive first pressure chamber to ambientas the full power pressure fluid is supplied to the then active secondpressure chamber and the piston starts to move; and decreasing of thestarting counter pressure in the then inactive first pressure chamber asthe piston leaves the end of the then active second pressure chamber sothat the piston is softly started at the end of the then active secondpressure chamber, wherein said decreasing of the starting counterpressure step includes the step of venting the counter pressure in thethen inactive first pressure chamber to ambient.
 2. A method ofcontrolling the function of a reciprocatable power machine as claimed inclaim 1:wherein said decreasing of the stopping counter pressure stepcommences at a point where the piston has completed about 95% of theactive power stroke.
 3. A method of controlling the function of areciprocatable power machine as claimed in claim 1:and further includingthe step of reducing the full power pressure of the pressure fluid inthe then active first pressure chamber as the piston reaches the end ofthe then inactive second pressure chamber concurrently with of thedecreasing stopping counter pressure in the then inactive secondpressure chamber.
 4. A method of controlling the function of areciprocatable power machine as claimed in claim 1:wherein saiddecreasing of the starting counter pressure step is completed at a pointwhere the piston has completed about 5% of the return stroke.
 5. Amethod of controlling the function of a reciprocatable power machine asclaimed in claim 1:wherein said decreasing of the startingcounter-pressure step includes the controlled opening of the theninactive first pressure chamber to ambient.
 6. A method of controllingthe function of a reciprocatable power machine as claimed in claim 1:andfurther including the step of increasing the pressure of the pressurefluid in the then active second pressure chamber to full power pressureas the piston leaves the end of the then active second pressure chamberconcurrently with the decreasing starting counter pressure in the theninactive first pressure chamber.
 7. A method of controlling the functionof a reciprocatable power machine as claimed in claim 1:wherein saiddecreasing of the stopping counter pressure step is performed stepwise.8. A method of controlling the function of a reciprocatable powermachine as claimed in claim 1:wherein said decreasing of the stoppingcounter pressure step is performed successively.
 9. A method ofcontrolling the function of a reciprocatable power machine as claimed inclaim 1:wherein said decreasing of the starting counter pressure step isperformed stepwise.
 10. A method of controlling the function of areciprocatable power machine as claimed in claim 1:wherein saiddecreasing of the starting counter pressure step is performedsuccessively.
 11. A method of controlling the function of areciprocatable power machine as claimed in claim 1:wherein saiddecreasing step decreases the stopping counter pressure in four stepscorresponding to a pressure difference of 50%, 25%, 5%, and 0% of thefull power pressure.
 12. An apparatus for controlling the function of areciprocatable power machine comprising:a cylinder having areciprocatable piston located therein and dividing said cylinder intofirst and second pressure chambers; and a valve system which controlsfluid pressures in said first and second pressure chambers, said valvesystem includinga valve poppet having a plurality of channels in order(a) to provide a full power pressure fluid to said first pressurechamber to move said piston in an active power stroke from an end of athen active said first pressure chamber to an end of a then inactivesaid second pressure chamber and to provide an evacuation of thepressure fluid from the then inactive said second pressure chamber, and(b) to provide an evacuation of the pressure fluid from the theninactive said first pressure chamber when said piston moves in a returnstroke, a building up means for building up a stopping counter pressurein the then inactive said second pressure chamber as said pistonapproaches the end of the then inactive said second pressure chamber tocounter-act the full power pressure of the pressure fluid in the thenactive said first pressure chamber, a decreasing means for decreasingthe stopping counter pressure in the then inactive said second pressurechamber to a positive final stopping counter pressure as said pistonreaches the end of the then inactive said second pressure chamber sothat said piston is softly stopped at the end of the then inactive saidsecond pressure chamber against the final stopping counter pressure, astarting means for utilizing the final stopping counter pressure tostart the return stroke of said piston from the end of a then activesaid second pressure chamber, a supply means for supplying the pressurefluid at a full power pressure to the then active said second pressurechamber after said starting means has started the return stroke of saidpiston to move said piston in an active return power stroke from an endof the then active said second pressure chamber to an end of a theninactive said first pressure chamber, a second starting means forproviding a starting counter pressure in the then inactive said firstpressure chamber as said piston starts to move from the end of the thenactive said second pressure chamber to counter-act the full powerpressure of the pressure fluid in the then active said second pressurechamber, and a second decreasing means for decreasing of the startingcounter pressure in the then inactive said first pressure chamber assaid piston leaves the end of the then active said second pressurechamber so that said piston is softly started at the end of the thenactive said second pressure chamber; wherein said first-mentionedstarting means furthercontrols an opening of the then active said firstpressure chamber to ambient to fully vent the full power pressure of thepressure fluid as said piston approaches the end of the then inactivesaid second pressure chamber, and closes the then inactive said firstpressure chamber to ambient as the full power pressure fluid is suppliedto the then active said second pressure chamber and said piston startsto move; and wherein said decreasing means vents the counter pressure inthe then inactive said first pressure chamber to ambient.
 13. Anapparatus for controlling the function of a reciprocatable power machineas claimed in claim 12:wherein said first mentioned decreasing meanscommences at a point where said piston has completed about 95% of theactive power stroke.
 14. An apparatus for controlling the function of areciprocatable power machine as claimed in claim 12:wherein said valvesystem further includes a reducing means for reducing the full powerpressure of the pressure fluid in the then active said first pressurechamber as said piston reaches the end of the then inactive said secondpressure chamber concurrently with the decreasing stopping counterpressure in the then inactive said second pressure chamber.
 15. Anapparatus for controlling the function of a reciprocatable power machineas claimed in claim 12:wherein said second decreasing means completesthe decreasing of the starting counter pressure step at a point wheresaid piston has completed about 5% of the return active power stroke.16. An apparatus for controlling the function of a reciprocatable powermachine as claimed in claim 12:wherein said second decreasing meanscontrols an opening of the then inactive said first pressure chamber toambient.
 17. An apparatus for controlling the function of areciprocatable power machine as claimed in claim 16:wherein said valvesystem further includes a second increasing means for increasing thepressure of the pressure fluid in the then active said second pressurechamber to full power pressure as said piston leaves the end of the thenactive said second pressure chamber concurrently with the decreasingstarting counter pressure in the then inactive said first pressurechamber.
 18. An apparatus for controlling the function of areciprocatable power machine as claimed in claim 12:wherein saiddecreasing means decreases the stopping counter pressure in four stepscorresponding to a pressure difference of 50%, 25%, 5%, and 0% of thefull power pressure.